Work vehicles, such as farm tractors and earthmoving machines, are frequently left in standby conditions with the engine idling. Such a situation occurs, for example, during work breaks, during the replacement or application of tools and during operations of hitching or unhitching trailers or sledges. In locations affected by very harsh climates, the vehicles are left idling overnight to avoid the risk of the oil and fuel becoming excessively cold.
Although the engine rotation speed under idling conditions is around 800-850 rpm, the fuel consumption and wear on mechanical parts are not, however, negligible. Thus engine control systems have recently been developed which, upon the occurrence of several operating conditions, further decrease the engine rotation speed to a second idle state, as low as 600-650 rpm.
The control systems presently available substantially work in this manner: each time the engine is left idling, a control unit runs a check on a series of operating parameters of the vehicle, e.g. activation of the parking brake, the absence of any commands on the operator's part, a zero forward travel speed, high voltage at the battery and high pressure at the oil pump. If one or more of the parameters listed above are satisfied, after a certain interval of time the control device lowers the engine rotation speed to the second idle state.
The control systems presently available thus carry out a check on a series of operating parameters of the vehicle before causing the engine to switch from idle to the second idle state. The operating parameters checked, however, offer a substantially indirect view of the vehicle's actual operating status. It is not always certain, in fact, that when the operating parameters remain in a certain state for a certain interval of time, this implies an actual possibility of switching to the second idle state of the engine. A typical case is represented by the moments in which the operator aboard the vehicle is engaged in technical conversations or in studying location plans or drawings and does not operate any controls on the vehicle. In such cases, it is necessary that at least the lighting and air conditioning devices remain on, and thus that the engine remain at idle without switching to the second idle state.
A further drawback of the control systems presently available is represented by the check, among the operating parameters checked by the control unit, on the elapsing of a given interval of time, measured by means of a timer. Essentially, before causing the engine to switch to the second idle state, the control unit checks that the operating conditions for switching to the second idle state are met up to the elapsing of a given interval of time. In many cases, that given interval of time is not necessary and substantially results in the engine remaining at idle pointlessly. Moreover, in many control systems the timer must be activated and set by the operator, with the risk that the operator will forget to activate it or set it on an incorrect interval of time.
The object of the present invention is to offer an engine control device which allows the drawbacks of the presently available control devices to be overcome.